The present invention relates to internal combustion engines, and more particularly to control system for controlling amount of secondary air to be supplied to the exhaust system of such engines.
For the purpose of purifying the exhaust gases from the conventional internal combustion engines, it is conventionally proposed to promote oxidation of noxious components, such as CO and HC, of the exhaust gases by an exhaust purifier, such as a thermal reactor or a catalytic converter, with the help of secondary air supplied to the exhaust system.
In the arrangement as above, a valve means is provided in a passageway, through which the secondary air that is induced into the exhaust system with variation of exhaust pressure flows, for closing the passgeway when the exhaust pressure is relatively high, while opening the passageway when the exhaust pressure is relatively low. This arrangement has a drawback that there is high possibility of overheating and, in fatal cases, damaging the exhaust purifier since even when exhaust gas temperature rises at high speed high load engine operating conditions, the secondary air is kept supplied to the exhaust system.